Voice communication in wireless systems has conventionally been provided via circuit-switched wireless telecommunication networks of the art, which allow a mobile unit to establish a fixed connection, or link, to the network via a radio bearer. However, as wireless technology evolves from voice-centric to data centric—a process begun in 3rd generation (3G) systems and expected to be completed with 4th generation (4G) systems, voice signals (along with data) are increasingly transmitted over a packet-switched network using a Voice over Internet Protocol (often referred to as VoIP).
For implementation of VoIP in a wireless telecommunication network, the speech data frames are embedded in Internet Protocol (IP) data packets. The IP packet headers may increase the size of the data packets that are transmitted by the wireless telecommunication network, thus somewhat reducing the capacity of a packet-switched wireless telecommunication network relative to a circuit-switched wireless telecommunication network. However, the IP packet headers may generally be compressed to reduce the overhead associated with transmitting speech data using VoIP. A commonly applied compression method, robust header compression (ROHC), reduces the size of the IP packet header by removing predictable and/or static information from the header. Using ROHC, the size of the IP packet header may be reduced by approximately an order of magnitude by reducing the information in the IP packet header to a sequence number, a context identifier, and a time stamp. Taking into consideration the packet payload, which is not compressed, the size of the total packet transmission (payload plus header) is reduced by approximately one-half by such ROHC compression.
Not all IP packet headers may be compressed. For example, it is generally necessary to send uncompressed or partially compressed IP packet headers when a mobile unit is being initialized or resynchronized, or when the network is recovering from an error. The uncompressed, or partially compressed, IP packet headers may include static and/or dynamic information that may be used to resynchronize the mobile unit or to recover from one or more transmission errors. Such static and/or dynamic information, usually characterized as “context” and usually sent for only the first few packets of a packet stream, provides context for the decompression of subsequent compressed packets of the packet stream. However, for mobile terminals located in weak signal areas, such as at a cell edge, the available signal energy, even at the terminal's maximum transmission power, may be insufficient to reliably transmit a packet having such context information included (in addition, of course, to the voice payload of the packet)